Treatment of oxide iron ores and other materials containing iron in oxide form



March 12, 1935. w. s. MILLAR 1,994,367

TREATMENT OF' OXIDE IRON ORES AND OTHER MATERIALS CONTAINING IRON IN OXIDE FORM Filed July 2, 1929 mhsam/#af M//r rmi INV ENTOR Patented Mar, l2, 1.935

TREATMENT 0F @MDE ERON GRES AND THER M'EEREALS CONTAINING IRON HN @XEDE FORM Application .lilly 2, 1929, Serial No. 375,572 lln Great Britain July 3, 1928 'n claims. (o1. es-zoo) it is Well known that the oxides of many metals may be converted into the chlorides of the metals by the action of chlorine gas, if the oxide is subjected to the simultaneous reducing action of carbon Thus, for example, ferric oxide is not attacked by chlorine, but if carbon is mixed with the oxide, and chlorine passed over the heated mixture, ferrous or ferrie chloride, or both, are formed,l together with carbon dioxide.

It has hitherto been thought that only carbon could be used to eiiect the reducing action and that the presence of sulphur and sulphides would be inimical to the chlorinating reaction, or at best, would not be productive oi any useful result in connection with this reaction. I have now found, however, as a result of experimental research, that so far from being inimical, sulphur and sulphides possess special advantages in many cases.

In accordance with the present invention, sulphur, sulphide of iron, or ore, mineral or other material containing iron and sulphur, such as pyrites, pyrrhotite, chalcopyrite, spent oxide, etc., is intimately mixed with oxide of iron, or mate-V rial. containing oxide of iron, such as pyrites cinders, other roasted ore or mineral, or naturally occurring oxide materials containing iron, and subjected, with or without drying, heating or other preliminary treatment, to the action of chlorine gas, or other gases or vapours containing chlorine, free or combined, such as chlorides of sulphur, ferric chloride, etc., with or without inert gases. V

In the simplest case, using ferrie oxide and pyrites as the oxide and sulphide materialsrespectively, the reaction may be expressedby the equation the products being ferrous chloride and sulphur dioxide.

With sulphur, the reaction proceeds according to the equation With chalcopyrite, pyrrhotite, and other sulphide minerals, the reaction is similar. Y

The gaseous product, when the proportions of reagents are selected in accordance with the above equations, is in all cases sulphur dioxide, which, may be employed in the manufacture of sulphuric acid, or for other known purposes. If

the chlorinating medium contains no inert gases,

the sulphur dioxide will be pure; if the chlorinating medium contains nitrogen, carbon dioxide, v

etc., these inert gases pass throughthe Vreaction chamber, and a dilute sulphur dioxide gas 1s obtained.

It is obvious that excess of sulphide material Where, as is. generally the case, the oxide or sulphide material (or both) contains non-ferrous metals, these are converted into the chlorides,

which may remainV with the ferrous chloride, or

pass lover with the gases,v according to their degrees of volatility, 'the' temperature of reaction and ythe volume of inert .gases present in'the chlorinating medium. Where such non-ferrous chlorides are volatilized, kthey may be separated from the gases by means ofV a suitable condenserV or settling chamber.

The mixture of ferrous chloride with chlorides.

of non-ferrous metals obtained as a result of the reaction -if chlorine be not used in excess may be dissolvedin water for separation of pure ferrous chloride, which may be subsequently electrolyaed` for recovery of metallic iron and chlorine. Alternatively, ferrie chloride may be formed from so .i

the ferrous chloride by treatment of the chloride mixture with air or oxygen, or with excess of chlorine, at a moderate temperature, say 250- 5G0 C., and thereby separated from thegangue and non-volatile chlorides; ferric chlorideso formed may then be oxidized by means of air or oxygen at high temperatures, say 5001000 C.,

with formation of pure ferric oxide and recovery of chlorine.

The chlorine recovered, either by electrolysis or oxidation, is equivalent in quantity to that used in chlorination, less the amount remaining combined with non-ferrous metals, and may be employed again, either directly or indirectly, for

rtreatment of Vfurther quantities of the oxide-sulphide mixture. Where the chlorine used is to be recovered by electrolysis, the mixture of ferrous chloride and chlorides of non-ferrous metals may be dissolved -in the minimum quantity ofV Water (or mother-liquor from a previous operal tion) at 80 C. or higher temperature. On being allowed to cool this solution separates pure ferrous chloride crystals which are used for the electrolytic bath. The mother-liquor is then freed from copper, if present, by precipitation with iron, and from lead, if present, by electrolysis between iron electrodes at a potential difference of about 1 volt or less. The mother-liquor is then used for dissolving further quantities of anhydrous chlorides at 80 or higher temperature, and this crystallization cycle repeated indefinitely. If zinc is present it will accumulate in the motherliquor by Vreason of the great solubility of the zinc chloride; in this case the cycle is repeated only until the liquor becomes so rich in zinc that .it becomes diiicult to wash the separated ferrous chloride crystals free from zinc chloride, at which point the liquor is withdrawn from the cycle and Worked up for recovery of zinc whilst the cycle is started afresh with water.

It will be seen that by my process I am able to obtain from any iron oxide-sulphide mixture, by a series of simple chemical operations, and

Without loss of chlorine, pure ferrie oxide or me-Y tallic iron, all the sulphur present for reducing the iron oxide as sulphur dioxide, and the nonferrous metals as chlorides.

VThe reaction may be carried out at any temperature from 200 C. upwards, but is most conveniently effected between 300 and 500 C. Sta tionary vfurnaces may be employed, but it will generally` be necessary in such cases, unless high proportions of gangue or inert material'are present, to admix coarse sand or inert material with the charge Yto avoid blockage by the chlorides formed. A rotating cylindrical furnace, in which the solid oxide-sulphide mixture is fed in at one end, and the solid chlorides are drawn off at the other, lower end, is very convenient; in this case, the chlorinating gases enter at the lower end, at which the solid chlorides are discharged, so that the re-agents move in counter-current to one another.

Where zinc and lead are present, it is advisable to `keep the temperature below 400 C., since the chlorides of these metals begin to be volatilized above this point, especially if inert gases are pres- Vcially suitable for treatment of pyrites cinders,

roasted sulphide ores, mattes, etc. since theseV generally contain oxides and sulphides present together, and it is a simple matter to bring the composition to the ratio of oxide to' sulphide required by the equation. Thus with pyrites cinders, which contain usually 3-4% of sulphur, or more if the pyrites has been roasted in lump burners, itv isnecessary to add only from 35-45 parts fresh pyrites to parts cinders, according to the compositions of the two materials and treat the mixture with the chlorinating medium; the sulphur is obtained as SO2, and the zinc, lead, copper etc. are obtained as chlorides. By the appropriate treatment of the chloride mixture formed, the chlorine used for xing the iron content as chloride is recovered, and the iron is obtained either as metaL'where the chloride is electrolyzed, or as oxide, where oxidation is employed, without use of any other raw material.

Since moisture'acts readily on the chlorides formed, yielding hydrochloric acid, which may cause loss of chlorine, it is desirable to dry the materials before treatment. In those cases Where the materials contain soluble salts, it may be de-Y oxide-sulphide mixture to give sulphur dioxide 1 and a material substantially free from oxygen,

4Fe2O3-f-14FeS2=22FeS-|6SO2 and in the second, treating with the chlorinating medium to obtain sulphur and the metal-chlorides,

, Y 15 x Whilst this two stage treatment has the advan` A tage that the sulphur dioxide gases( are obtained,`

by the first operation, so that therev is no possibility of adrnixture with chlorine, and free sulphur is obtained in the second stage, a higher proportion of sulphide material is required, and correspondingly greater quantities of chlorides must be handled. In this case, however, no preliminary drying of the oxide-sulphide mixture is required.'

The process as a whole is strongly exothermic, and the desired temperature is readily maintained by regulating the rates `of admission of Ythe rev agents. admission of the chlorinating medium has to be controlled; in a rotating furnace, the rate of admission of the oxidesulphide mixture may also be regulated.

The attached iiow sheet illustrates one method of carrying out the invention, in which the chlorinating medium is recovered by oxidation. In this form, the mixture of oxides and sulphides is treated first with only suiicient chlorinating medium to convert the iron present into ferrous chloride, the other metals present being also converted into chlorides. The mixture so obtained is treated with a further quantity of chlorinating medium, suflicient to convert the ferrous chloride into ferric chlo-ride; this is volatile at a relatively low temperature, and therefore may readily be separated from the gangue and chlorides of non-ferrous metals. The separated ferric chloride is finally oxidized, yielding ferric oxide and chlorine; more.

In a stationary furnace, only the rate of or less ferric chloride lmay be left unchangedby v using less than the theoretical amount of oxygen. The chlorine recovered is employed again, both for the first chlorination of the oxide-sulphide mixture, and for conversion of the ferrous chloride so obtained into ferrie chloride.

I claim:

l. A process of treating materials containing materials containing amount of sulphur-containing material so admixed so as to insure that suflicient Vsulphur is present in theV mixture thus formed to combine v iron oxide to form sulphur dioxide, and `to formV chlorides of iron and the non-ferrous metals present.

2. A cyclic process of treating oxide-sulphide mixtures containing iron and non-ferrous metal values, consisting in adjusting the proportionsof sulphide to oxide materials present so as to insure that sufficient sulphur is present in the mixture to reduce the oxidesfand form with the oxygen content thereof-sulphur dioxide, treating Vtheffadjusted' mixture Avat'lan elevated temperature sufficient to promote reaction ofthe sulphide sulphur with the oxides present andA with. a chlorinating medium to form non-ferrousvchlorides.and iron chloride, separating the non-ferrous` chlorides from the iron chloride-formed,l treating-such iron chloride fortherecovery of,v chlorinating medium, and'utilizing such chlorinatingmediumfor the treatment or further-` quantities of oxide-sulphide mixture.

3; -A cyclic process of-treating voxide-sulphide mixtures containing iron, consistingv irl-treating such mixtures with a chlorinating medium to form non-ferrous chlorides and iron chloride, separating the? non-ferrous chlorides from the iron chloride formed, electrolyzing. such iron chloride for the recovery of` chlorinating medium, and utilizing such chlorinating medium for the treatment of further quantities of oxide-sulphide mixture.

4. Acyclic process of treating oxide-sulphide mixtures containing iron, consisting in adjusting the proportions of sulphide to oxide materials present so as-to insure'that suicient sulphur-is present in the mixture to reduce the oxides and form with the oxygen content thereof sulphur dioxide, treating the adjusted mixture at an elevatedftemperature suflicient to-promote reaction oflthe sulphide sulphur vwith'the oxides present and with a chlorinating `medium to `form nonferrous'chlorides and iron chloride, separating the non-ferrous chlorides from the iron chloride formed, subjecting such iron chloride to oxidation for the recovery of chlorinating medium, and utilizing such chlorinating medium'forf theftreatment of further quantities of` oxide-sulphidernixture.

5. A process of treating materials containing iron oxide which comprises admixing therewith materials containing sulphur and heating "the mixture thus formed with a chlorinating medium whereby to obtain sulphur dioxide, the chlorides of iron and the non-ferrous metals present,regu lating the proportion of the chlorinating medium and the operating temperature so that substantially the whole of the iron present is obtained in thesolid condition as ferrous. chloride, treating such ferrous chloride for recovery of a chlorinating.` medium, and utilizing such chlorinating medium for the treatment of further `quantities of oxide-sulphide mixture.

6. A process of treating materials containing iron :oxide which comprises admixing'therewith materials containing sulphur and heating the mixture thus formed with a chlorinating medium whereby to obtain sulphur dioxide, the chlorides of iron and the non-ferrous metals present, regulating the proportion of chlorinating medium and the operating temperature so that substantially the whole of the iron present is driven oir in the volatile form as ferric chloride, treating such ferric chloride for recovery of a chlorinating medium, and utilizing such chlorinating medium for the treatment of further quantities of said mixture.

'7. A process of treating materials containing iron oxide which comprises admixing therewith materials containing sulphur, heating the mixture thus formed with chlorine-containing gases at a temperature above 200 C. whereby'to obtain sulphur dioxide, the chlorides of iron and the non-ferrous metals present, separating the non-ferrous chlorides from the iron chlorides formed, treating such iron chlorides for the recovery ofza chlorinating me`dium,vand utilizing such chlorinating-medium for the treatment of further quantities of said mixture.

8. A process of treating materials containing iron oxide which comprises admixing therewith materials containing sulphur, heating .the mixture rto `drive ofi moisture and other volatile bodies, subjecting! the residue to the action of a chlorinating .medium in such proportion and lat a temperature such as to obtain substantially the` medium and the'operatingtemperature so that v substantially the whole of the iron present in the mixture is obtained in the solidcondition. as ferrous chloride and said non-ferrous metal valueshave been changed to chloride form, subjecting the mixture of chlorides containing ferrous chloride to the action of: chlorine kto form and'volatilize ferrie chloride, treating such erric chloride for recovery of a chlorinating medium, and utilizing such chlorinating Ymedium for the treatment of further quantities of said mixture.

10. A process of treating materials containing iron oxide and chlorinatable values of rhonderrous metals,.which comprises admixing therewith materials containing sulphur and heating the mixture thus formed with a chlorinating medium,

regulating the proportion of the chlorinating.

medium and the operatingtemperature so that substantially the whole of the iron present in the mixture is obtained in the solid condition as ferrous4 chloride and said non-ferrous metal values have been changed to chloride form, subjecting the mixture of chlorides containing ferrous chloride to the action of limited quantities of gases containing oxygen at a moderate temperature to ormand volatilise ferrie chloride, treating such ferric chloride for recovery of a chlorinating medium, and utilizing such-chlorinating medium for the treatment of further quantities-of said mixture.

11..A process of treating materialscontaining iron oxide and chlorinatable values of non-ferrous metals, which comprises admixing therewith materials containing sulphur and heating the mixture thus formed with a chlorinating medium, regulating the proportion of the chlorinating medium and the operating temperature so that l substantially the whole of the iron present in the mixture is obtained in the solid condition as ferrous chloride and said non-ferrous metal values have been changed to chlorideY form, subjecting the mixture of chlorides containing ferrous chlo-l ride to oxidizing action at a temperature between 250 C. and 550 C. to form and volatilize ferric chloride, treating such ferrie chloride for recovery of a chlorinating medium, and utilizing such chlorinating medium for the treatment of further quantities of said mixture.

12. A process of treating materials containing iron oxide and chlorinatable values of non-ferrous metals, which comprises admixing therewith materials containing sulphur and heating the materials containing sulphur and heating the mixture thus formed with a chlorinating medium, regulating the proportion of the chlorinating medium and the operating temperature so thatsubstantially the whole of the iron present in the mixture is obtained in the solid condition as ferrous chloride and said non-ferrous metal values have been changed to chloride form, subjecting the mixture of chlorides containing ferrous chloride to the action of limited quantities of oxygen at a moderate temperature to :formv and volatilize ferric chloride at a temperature between 250 C. and 550 C., treating such ferrie chloride for recovery of a chlorinating medium, and utilizing such chlorinating medium for the treatment of Ifurther quantities of said mixture.

13. 'A process of treating materials containing iron oxide and chlorinatable values of non-ferrous metals, which comprises admixing therewith materials containing sulphur and heating the mixture thus formed with chlorinating medium, regulating the proportion of thechlorinating medium and the operating temperature so that `substantially the whole of the iron present in the mixture is obtained in the solid condition .as ferrous chloride and said non-ferrous metal values have `been changed to chloride form, subjecting the mixture of chlorides containing ferrous chloride to oxidation to form ferrie chloride, oxidizing the ferric chloride at high temperatures to form pure ferric oxide and regenerate" chlorine, and utilizing such chlorine for the treatment of further` quantities of said mixture.

V14. A process `of treating materials containing iron oxide and chlorinatable values of non-ferrous metals, which comprises admixing therewith materials containing sulphur and heating the mixture thus formed with a chlorinating medium, regulating the proportion of the chlorinating medium and the operating temperature so that substantially the whole of the iron present in the mixture is obtained in the solid condition as ferrous chloride and said non-ferrous metal values have beenl changed to chloride form, subjecting the mixture of chlorides containing ferrous chloride to oxidation to form ferrie chloride, oxidizing such ferrie chloride at a temperature between 600 C. and 1200 C. to form ferrie oxide and regenerate chlorine, and utilizing such chlorine for the treatment of further quantities of said mixture.

. 15. A process of treating materials containing iron oxide andchlorinatable values of non-ferrous metals, which comprises adrnixing therewith mixturethus formed with a chlorinating medium,

regulating the proportion of chlorinating medium u and the operating temperature so that substan-l tially the `whole of the ironpresentin the mixture is driven off in the lvolatilefform as ferric chloride, recovering the non-ferrous chlorides, from the residue by extraction with aqueous solvent, treating the ferrie chloride driven 01T forv recovery of a chlorinating medium, and utilizing` Y Y with materials containing sulphur and heating'`A the mixture thus formed with a chlorinatingmeit'Y diurn, regulating the proportion of chlorinatingV medium so that substantially `the Vwhole of theV iron present in the mixture'is obtained as,fer,

rous chloride,` dissolving the mixture of ,chlorides obtained in the minimum quantity, ofr sol-l vent at a Atemperature of at least 80 C., cooling down to cause separation of pure ferrous'chlog ride crystals, dissolving such pure ferrous-chloride crystals, electrolyzing the solution to recover chlorine, and utilizingsuch chlorine for the treatment of further quantities of said mixture.

17. A process of treating materials containingiron oxide and chlorinatable values kof copper,

lead and zinc, which comprises admixing therewith materials-containing sulphurV and heatingV the mixture thus formed with achlorinating medium, regulating the proportion of chlorinating/ medium so that substantially the whole of the iron present in the mixture is obtained as ferrous chloride and the values of copper, lead andzinc have been changed to chloride form, dissolving the" mixtureof chlorides obtained in theminimum quantity of solvent at a temperature of at least 80 C., and coolingl down to cause separation of pure ferrous chloride crystals, freeing the solvent from;

copper after separation of ferrous chloride crystals by precipitation with iron, andY from lead,

by electrolysis between iron electrodes at an E. M. F. of about 1 volt or less, using the solventr to dissolve further quantities of the anhydrousr chlorides, repeating the cycle until thek solvent is rich in zinc, dissolving the separated ferrous chloride crystals, electrolyzingthe solution torecover chlorine, and utilizing such chlorine for the treatment of further quantities of said mixture.

WILLIAM SoM-ERVLLLE Minnen.v 

